linux-kernel - Re: [PATCH] ipv4/mptcp: fix divide error

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Date:   Tue, 24 Aug 2021 09:36:35 +0200
From:   Matthieu Baerts <matthieu.baerts@...sares.net>
To:     Jiang Biao <benbjiang@...il.com>,
        mathew.j.martineau@...ux.intel.com, davem@...emloft.net,
        kuba@...nel.org
Cc:     netdev@...r.kernel.org, mptcp@...ts.linux.dev,
        linux-kernel@...r.kernel.org, benbjiang@...cent.com,
        Jiang Biao <tcs_robot@...cent.com>
Subject: Re: [PATCH] ipv4/mptcp: fix divide error

Hi Jiang,

On 24/08/2021 09:19, Jiang Biao wrote:

(...)

> There is a fix divide error reported,
> divide error: 0000 [#1] PREEMPT SMP KASAN
> RIP: 0010:tcp_tso_autosize build/../net/ipv4/tcp_output.c:1975 [inline]
> RIP: 0010:tcp_tso_segs+0x14f/0x250 build/../net/ipv4/tcp_output.c:1992

Thank you for this patch and validating MPTCP on your side!

This issue is actively tracked on our Github project [1] and a patch is
already in our tree [2] but still under validation.
> It's introduced by non-initialized info->mss_now in __mptcp_push_pending.
> Fix it by adding protection in mptcp_push_release.

Indeed, you are right, info->mss_now can be set to 0 in some cases but
that's not normal.

Instead of adding a protection here, we preferred fixing the root cause,
see [2]. Do not hesitate to have a look at the other patch and comment
there if you don't agree with this version.
Except if [2] is difficult to backport, I think we don't need your extra
protection. WDYT?

Cheers,
Matt

[1] https://github.com/multipath-tcp/mptcp_net-next/issues/219
[2]
https://patchwork.kernel.org/project/mptcp/patch/286de8f451b32f60e75d3b8bcc4df515e186b930.1629481305.git.pabeni@redhat.com/
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